1. Field of the Invention
The present invention generally relates to data storage devices such as tape and disk drives and, more particularly, to linear actuators or voice coil actuators that are used to position tape heads relative to recording media in tape and disk drives.
2. Relevant Background
Tape drives have been widely employed in industry for over thirty years due to their ability to store large amounts of data on a relatively small and inexpensive removable format. Typically, a removable cartridge holding a reel or spool of storage tape is initially loaded into a tape drive. After coupling the storage tape on the cartridge reel to a take-up reel of the tape drive (e.g., via respective leaders), the tape is unwound from the cartridge supply reel, moved past one or more tape head assemblies (e.g., each having one or more tape heads with one or more read/write/servo elements/transducers in the case of magnetic tape) or optical pickup units (OPUs) (e.g., in the case of optical tape) for reading and/or writing of data, and wound onto the take-up reel via a drive motor. Next, the tape is unwound from the take-up reel, moved past the tape heads or OPUs, and wound onto the cartridge. The storage tape is uncoupled from the take-up reel prior to removing the cartridge from the tape drive.
A head assembly of a tape or disk drive typically includes a number of positioning subassemblies that allow a servo control system of the drive to accurately position the one or more heads relative to the recording media (e.g., to magnetic tape or disks) in a number of different manners. For instance, one positioning subassembly may include a coarse linear motor and corresponding travel carriage that is configured to linearly move the one or more tape heads in a lateral (e.g. perpendicular) direction relative to the direction of motion of the media. Another positioning subassembly of a tape or disk drive may include a rotary actuator that is configured to angularly position the one or more tape heads relative to the recording media (and the coarse travel carriage) about an axis that is perpendicular to the recording media (e.g., to the magnetic tape) as well as to the direction or path of motion of the recording media. The angular head motion allows the servo readers and/or the read/write elements on the head to be aligned correctly to the media during track following and/or during read/write operations. For instance, the rotary actuator may be attached to a read/write head by means of a carriage (e.g., the fine travel carriage) or other supporting structure.
Another positioning subassembly may include a linear (e.g., voice coil) actuator and corresponding travel carriage that is configured to linearly move the one or more tape heads relative to the coarse travel carriage and in a lateral direction relative to the direction of motion of the media (e.g., along an axis that is perpendicular to the direction of motion of the media) over a finer range of motion than that of the coarse travel carriage. Conventional linear actuators often include a linearly movable, electrically conductive coil having a plurality of windings that are disposed relative to a pole of a stationary magnet. Upon energizing the coil with an analog control signal (e.g., a DC bi-directional control signal), the head may be linearly moved (e.g., via magnetic flux paths between the coil and the magnet) to position the head relative to the recording media.
The coil of many voice coil actuators has significant mass in relation to that of the head assembly. As the mass of the coil is often broadly distributed about the actuation axis of the voice coil actuator, movement of the coil can result in out-of-plane resonant vibrations leading to instability, bandwidth reductions, and negative effects on tape head performance. Furthermore, the flexible printed circuit (FPC) that energizes the moving coil adds mass to the coil that is asymmetrical relative to the actuation axis and thus can result in out-of-plane resonances. Still further, FPCs are subject to fatigue failure caused by repeated cycling of the linear actuator.